Certain organisms including plants and some microalgae use a type II fatty acid biosynthetic pathway, characterized by the use of discrete enzymes in a multimeric complex for fatty acid synthesis. In contrast, mammals and fungi use a single, large, multifunctional protein.
In organisms that use a type II fatty acid biosynthetic pathway, β-ketoacyl-ACP synthase I (KAS I, EC 2.3.1.41) is one of the enzymes responsible for elongation of growing medium-chain fatty acyl-ACP from 4 to 16 carbon atoms in length. KAS I uses C2-C14 acyl-ACPs as substrates for condensation with a C2 unit derived from malonyl-ACP. KASIV is a related enzyme that serves a similar elongation function. Thus, KASI and KASIV can both be considered KASI-like enzymes.
Such genes have been introduced to plants using recombinant DNA technology. See for example U.S. Pat. Nos. 7,301,070, 6,348,642, 6,660,849, 6,770,465 and US2006/0094088 (of which ¶¶194-200 and the entirety of the document are hereby incorporated herein by reference). In plastidic cells such as those from plants, macroalgae and microalgae, KAS I-like enzymes are located in the chloroplasts or other plastids together with other enzyme of the fatty acid synthesis (FAS) pathway.
PCT publications WO2010/063032, WO2011/150411, WO2012/106560, and WO2013/158938 disclose genetic engineering of oleaginous microalgae including targeting of exogenous FAS gene products to the microalgal plastid.